Method and apparatus for copying



Feb. 1, 1966 w. WILLMOTT 3,232,190

METHOD AND APPARATUS FOR COPYING Filed June 28, 1963 INVENTOR ROBERT W. WILLMOTT ATTORNEY.

United States Patent The present invention relates generally .to the document copying art and more particularly to an improved method and apparatus for applying toner to a surface having an electric charge pattern thereon corresponding to the visual information on a master document being copied.

As will be understood by those skilled in the art, a well known process of copying documents comprises the use of a photoconductor formed to define a continuous recording medium, such as a drum or a belt, which is moved withrespect to a plurality of stations. At a first station, the photoconductor is exposed to an electric field and assumes-a uniform, relatively high potential. The photo- ;conduc'tor then moves past a second station where a light image-of the master document being copied is projected on the photoconductor. The photocon-ductor now has a charge-pattern thereon corresponding to the visual information on the master document. At the next station, a toner material is applied over the entire photoconductor regardless of the fact that only some areas of the photoconductor remain at a relatively high potential. The ten er is either dropped or cascaded over the photoconductor or agitated in a suitable chamber so that particles of the toner are suspended in the chamber atmosphere through which the photoconductor must pass. In theory, the toner particles cling and adhere to those areas of the photoconductor which are at a relatively high potential to create a toner image corresponding to the master document. This toner image is then transferred to a suitable support at the succeeding station to define a copy of the master document. Thereafter, the photoconductor moves to a cleaning station where any remaining toner is removed and then to the first or initial charging station where the process is begun again.

While the above described copying process is widely employed at the present time, it is subject to certain problems which have somewhat limited the application there- 'of. The pulverulent and powder-like toner comes in direct contact with all areas of the photoconductorincluding those areas which are at a relatively low potential. A relatively low potential remains on the photographical- 1y exposed areas of the photoconductor which have been illuminated with a large amount of light and represent the background. A certain amount of the toner, and particularly the smaller size particles thereof, is attracted and held to these areas. This toner is transferred to the suitable support along with the toner representing the visual information on the master document and a copy is provided which appears dirty due to streaks or smears in the background. This background noise detracts from the quality and overall appearance of the copy, as should be readily apparent. The above problem has long been recognized in the art but no completely satisfactory solution has been proposed.

Briefly, the present invention relates to method and apparatus for applying toner to a surface having a charge pattern thereon corresponding to the visual information on a master document which is being copied. The toner is applied only to the areas of the surface representing the visual information and does not contact the remaining areas of the surface. In the illustrated embodiments of the invention, a thin layer of toner is positively held and maintained in spaced relation with respect to the surface. The relatively high potential of certain areas of the surface exert electrostatic forces of sufficient intensity to overcome the forces holding the toner in the thin layer and toner particles are attracted to these areas. The electrostatic forces exerted by the remaining areas of the surface are insufficient to overcome the forces maintaining the toner in a thin layer and these areas do not receive any toner. Background noise, such as streaks and smears, is eliminated on the copy since toner does not come in contact with the areas of the surface correspond ing to the background areas of the master document.

The density of the final copy is easily and accurately controlled. This is accomplished by providing means for adjusting the spacing or distance between the charged surface and the thin layer of toner. In one embodiment of the invention, a thin layer of toner is held by electrostatic forces to a toner backing material and the copy density can also be controlled by varying the potential on the toner backing material.

It is the primary or ultimate object of the invention to provide method and apparatus for copying wherein toner material is applied only to selected areas of a surface having a charge pattern thereon corresponding to the visual information on a master documentbeing copied. A thin layer of toner is maintained in spaced relation with respect to the surface and only those areas of the surface which have a potential sufficient to exert electrostatic attractive forces capable of overcoming the forces maintaining the layer of toner in spaced relation receive the toner. The remaining areas of the surface do not receive toner so that background noise does not appear in the finished copy.

Another object of the invention is the provision of method and apparatus for copying wherein the density of the finished copy can be accurately controlled and easily adjusted. This is accomplished by varying the spacing between the charged surface and the thin layer of toner and/or varying the forces tending to maintain the toner in the thin layer. Such density control is accomplished without in any way altering or changing any other step in the copying process and is simple to implement.

A further object of this invention is to provide method and apparatus for copying wherein the toner is stored in an improved form and the replenishment of the toner supply in a copy machine is greatly simplified. In a second embodiment of the invention, a thin layer of toner is held on a toner backing material by a suitable adhesive. The toner coated backing material is stored in the copy machine in roll form. To replenish the toner supply in a copy machine it is only necessary to remove a used roll and insert a new roll. Such replacement is a relatively clean and simple operation which contrasts sharply with the time consuming and messy job presently encountered by a service man in pouring toner powder in the hopper or trough holding this powder in prior art machines.

A still further object of the invention is the provision of method and apparatus of the type above described which are characterized by their extreme simplicity and high reliability. The toner coated backing material is advanced at a slow rate with respect to the charged photoconductor by conventional drive means. Also, the means guiding the toner coated backing material is easily moved toward and away from the photoconductor surface to control the density of the finished copy.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a schematic side view showing copying apparatus constructed in accordance with and embodying the teachings of the present invention.

FIGURE 2 is an enlarged view of a portion of the apparatus shown in FIGURE 1: illustrating specifically the apparatus employed for adjusting the spacing between the toner coated backing material and the charged photoconductor; and

FIGURE 3 is a schematic side view similar to FIGURE 1 showing a second embodiment of the invention.

Referring now to the drawings, and initially to FIG- URE 1 thereof, the reference numeral designates generally a copy machine comprising a drum 11 having an outer surface 12 of any suitable photoconductor, such as a layer of photoconductive insulating selenium. It should be understood at the outset that the teachings of the present invention are not limited to the use of any particular photoconductor. The drum Ill is rotated in the direction indicated by arrow 13 by motor 14 acting through a suitable drive connection 15, such as a belt.

Disposed around the circumference of the continuous photoconductor surface 12 are a plurality of spaced processing stations. In order of operation, the first of these stations is a charging station 17 comprising, for example, a corona discharge device. This device may include one or more fine corona generating wires 18 mounted within a shield 19 and connected by lead 20 to an appropriate high voltage corona discharge source, not shown. The wire is maintained at a corona generating potential (approximately 7000 volts for selenium) with respect to shield 19 so that the photoconductor is charged to a uniform and relatively high potential.

The next station in the direction of rotation of the drum 11 is an exposure station 22. The exposure station shown comprises an exposure slit 23 and lens 24 and is adapted to focus an image of a master document, not shown, appearing at slit 23 on the surface of the photoconductor. The disclosed exposure station is representative only and any of a Wide variety of systems capable of forming an image of the master document on the photoconductor can be employed. The areas of the photoconductor which receive the greatest amount of illumination, representing the lighter document background, are discharged to a greater extent than the areas of the photoconductor which are illuminated to a lesser extent. The photoconductor has an electrostatic charge pattern thereon with a potential difference existing between those areas representing the background and those areas representing the visual information of the master document.

Positioned next in the direction of rotation of the drum 11 is a toner station 26 to which the electrostatic image on the photoconductor is presented. This toner station is particularly important in accomplishing the objects of the present invention and comprises a roll of toner backing material 27 mounted on a supply reel 28. The toner backing material is a thin material arranged in such a manner that an electrostatic charge will distribute itself essentially evenly over its surface. A preferred embodiment would be an insulating paper with minute parallel conductive paths running the length of the paper. The toner backing material is fed from the supply roll to a take-up reel 29 via a pair of guide rolls 3%) and 31. The take-up reel 29 is driven by a motor 32 and the guide rolls 30 and 31 can also be driven if desired. It is preferred that a back tension device, such as a friction slip brake, not shown, be provided for supply reel 28 so that the toner backing material is maintained in tensioned relation With respect to the guide rolls 30 and 31.

The guide roll 30 is received in nesting relation in a U-shaped trough 35 Which contains a quantity of toner 36. The toner may be of the pigmented or dyed electrostatic powders well known in the art. The arrangement is such that the toner backing material 27 is caused to move through the trough 35 and comes in intimate contact with the toner 36. An electric charge is placed on the outer surface of the toner backing material 27 unwound from the supply roll by suitable apparatus schematically indicated as comprising a lead 38 and an adjustable potenpend on the particular photoconductor employed and this determines the polarity of the charge induced on the surface of the toner backing material. The electrostatic charge on the toner backing material 2'7 causes particles of the toner to be attracted and held to this backing material as the same passes around roll 30 and into con tact with the toner 36 in trough 35. As shown in FIG- URE 2 of the drawings, a thin layer of toner 40 of substantially constant thickness and density is attracted and held to the outer surface of the toner backing material. The backing material 27 having a thin layer of toner 40 thereon moves about guide roll 31 in closely spaced relation with respect to the photoconductor 12 on drum 11. It is important to note that a small air gap 42 exists between the coated backing material and the photoconductor. As previously explained, the charge on the outer surface of the backing material 27 has a polarity opposite the polarity of electrostatic image on the photoconductor. The charge on the outer surface of the backing material tends to hold the layer of toner 4t) on the backing material. Within the small air gap 42, the areas of the photoconductor which are at a relatively high potential create an electrostatic field which is sufiicient to cause particles of the layer of toner 40 to jump across the gap and become attached to these areas of the photoconductor. However, the remaining areas of the photoconductor do not cause an electrostatic field suflicient to overcome the electrostatic forces holding the toner to the backing material. Toner is attracted to and held on the areas of the photoconductor which are at a relatively high potential and represent the visual information on the master document. The toner does not come in contact with the remaining areas of the photoconductor so that background noise never appears in the final copy. 7

Only a small portion of the available toner on the backing material is transferred to the photoconductor at any one time. It is preferred that the toner coated backing material be advanced at a slow rate with respect to the speed of rotation of the drum. This can be accomplished by proper selection and control of the motors 14 and 32 driving the drum 11 and the take up reel 29, re-

spectively. In this manner, more effective utilization of' the toner coated backing material is achieved.

The amount of toner attracted to the selected areas of the photoconductor and, as a result, the density of the copy, is controlled within limits by varying the size of the air gap and/ or the electrostatic potential applied to the outer surface of the toner backing material. As most clearly shown in FIGURE 2 of the drawings, the guide roll 31 has the ends of its mounting shaft 44 journaled in bearings 45 which in turn are movable in longitudinal slots 46 formed in end plates 47. Rods 48 are threadably received in the end plates and control the position of the'guide roll 31 with respect to the photoconductor surface 12 of the drum. The bearings 45 are maintained against the forward ends of the rods 48 by a pair of compression springs 49. By adjusting either the position of the guide roll 31 by turning rods 48 or adjusting potential source 39, the forces occurring in air gap 42 tending to attract the toner to the photoconductor surface can be accurately controlled. These adjustments, either singularly or in combination, regulate the amount of toner deposited on the areas of the photoconductor which are at a relatively high potential. It should be noted that these adjustments are made at the toner station and the operation of the initial charging and exposure stations 17 and 22 is not altered in any manner.

4 An optional arrangement with respect to the apparatus shown in FIGURE 1 of the drawings is to employ a toner backing material 27 which is an insulating material, such as. Mylar, certain paper or the. like, and deposit an electrostatic charge on the surface of guide roll 31 by a separate corona discharge device shown in broken lines and indicated by reference numeral 50. A charge of opposite polarity to that on the backing material is placed on the guide roll 3-1 and has the effect of decreasing the attractive force between the toner and the backing material. This decrease allows the toner particles to be attracted to the areas of the photoconductor where relatively-high potential exists. The advantage of this arrangement is that the charge placed on the backing material 27 may have a potential which is somewhat independent of the charge on the photoconductor 12 and the size of the air gap 42 and sufficient to insure that the toner positively stays on ,the backing material as the backing material moves from the toner trough 35 to the guide roll 31'. Also, thepotentialplaced on the guide roll 31 by discharge device 50 can be adjusted to provide yet another means for controlling the density of the final copy. When insulating toner backing material 27 is employed, as in this optional arrangement, the initial electrostatic charge may be deposited onthe backing material'by an adjustable corona discharge device 57 shown by broken lines in FIGURE 1 or" the drawings. The discharge deviee 57 would replace lead '38 and source 39 in this case. I

Positioned next in the direction of rotation of the drum is a transfer station 51. At this station the toner image is transferred to a web 52 of paper or other suitable material which is moved in a desired path by guide rolls 53 from supply roll 54 to take up roll 55. A corona discharge device 56'is positioned opposite the point of contact between the web 52 and the drum to aid in the transfer of the image to the web. The web is moved to a fixing station where the toner image is permanently affixed to the web. This may comprise an infrared radiating lamp 57 adapted to project sufiicient heat on the surface of the web 52 to melt the toner thereon. Other fixing techniques can be employed as will be apparent to those skilled in the art.

The last station in the operational cycle of the copy machine is a cleaning station 60 comprising a rotating brush 61 of suitable fibrous material. The brush is rotated by drive motor 14 and is adapted to remove any residual toner left on the'photoconductor which was not transferred to the web 52 at the transfer station 51.

A second embodiment of the invention is shown in FZGURE 3 of the drawings and, to avoid unnecessary repetition in the specification, component parts which are similar to those disclosed in connection with the first embodiment are indicated by corresponding primed reference numerals and will not be further described. The main difference in the apparatus shown in FIGURE 3 is the arrangement of the toner station 70. A toner backing material 71 is coated with a suitable adhesive and then a thin layer of toner is applied thereto. The toner is held to the outer surface of the backing material by the adhesive so that the apparatus for applying an electrostatic charge on the outer surface of the backing material and a supply of toner in loose powder form are not required.

The toner coated backing material 71 is fed from a supply roll 72, past the guide roll 31' and to take up roll 73. The electrostatic forces in the area gap 42' exerted by the areas on the photoconductor which are at a relatively high potential are sufficient to pull the toner free from the adhesive on the backing material to these areas. However, the adhesive exerts a sufficient force to prevent the toner from being pulled to the other areas of the photoconductor. This embodiment has a significant advantage in that no toner in loose powder form is used in the copy machine. To replenish the toner supply in the machine it is only necessary to remove a used take up roll of toner coated backing material and insert a new supply roll. This operation is extremely simple and clean when comparcdwith the operations required in serving machines where the loose toner is maintained in a hopper or trough. The density of the copy is controlled in this case by adjusting the position of guide roll 31 to vary the size of the air gap 42'. I

It should now be apparent that the objects initially set forth have been accomplished. Of particular importance in. the provision of method and apparatus for copying Where the toner comes in contact only with the areas on a charged surface corresponding to the visual information on a master document being copied. This eliminates background noisewhich characterizes copies produced by prior art copy machines of the disclosed type.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the 'art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is: a h

1. Apparatus for creating a copy of a master document comprisingr Q a photoconductor and a plurality of processing stations;-

5 means to effect relative movement between said photoconductor and saidstations;

" a first of said stations comprising means for establishing a uniform electrostatic charge of one polarity on said photoconductor; p

' a second of said stations comprising means for projecting an image of said master document on said photoconductor to create an electrostatic charge pattern having areas of relatively high potential of said one polarity corresponding to the visual information on said document;

a third of said stations comprising a thin layer of toner material spaced from said photoconductor solely by an air gap;

means for maintaining said thin layer of toner material in spaced relation with r'e's pect to said photoconductor; and

only said areas of relatively high potential of said one polarity on said photoconductor exerting sufficient electrostatic forces to overcome said means for maintaining and causing said toner material to move across said air gap to said area's whereby toner material does not come in contact with the remaining areas of said photoconductor and a toned image corresponding to said visual information on said master document is created on said photoconductor.

2. Apparatus according to claim 1 further characterized by:

said means for maintaining said thin layer of toner material in spaced relation with respect to said photoconductor comprises a toner backing material;

means for establishing an electrostatic charge of the other polarity on said toner backing material; and

said electrostatic charge on said toner backing material tending to hold said thin layer of toner material to said toner backing material.

3. Apparatus according to claim 1 further characterized by:

said means for maintaining said thin layer of toner material in spaced relation with respect to said photoconductor comprises a toner backing material; and

an adhesive on said toner backing material tending to hold said thin 'layer of toner material to said toner backing material.

4. Apparatus for creating a copy of a document comprising:

a surface having an electrostatic pattern of one polarity thereon corresponding to the information on the document being copied;

said electrostatic pattern having areas of relatively high potential and the remaining areas being at a relatively low potential;

7 means for transferring toner material to said surface to create a pattern of toner material on said surface corresponding to said electrostatic pattern and said information on said document being copied;

said means for transferring comprising a supply of toner material spaced from said surface solely by an air gap;

means for maintaining said supply of toner material in spaced relation with respect to said surface;

said areas of relatively high potential of said electrostatic pattern exerting electrostatic forces of suflicient magnitude toovercome said means for maintaining and causing toner material to move across said gap to said areas of relatively high potential; and

said remaining areas exerting electrostatic forces which are insufiicient to overcome said means for maintaining whereby toner material does not move across said air gap and come in contact with said remaining areas.

5. Apparatus according to claim 4 further characterized by:

said means for maintaining comprises electrostatic means.

6. Apparatus according to claim 4 further characterized by:

a toner backing matterial; and

said means for maintaining comprises an adhesive on said toner backing material.

7. Apparatus according to claim 4 further characterized by:

means to adjust the size of said gap between said supply of toner material and said surface to control the amount of said toner material deposited on said areas of relatively high potential.

8. Apparatus for creating a copy of a document comprising:

a surface having an electrostatic charge pattern of one polarity thereon corresponding to the information on the document being copied;

said electrostatic charge pattern having areas of relatively high potential and the remaining areas being at a relatively low potential;

means for transferring toner material to said surface to create a pattern of toner material on said surface corresponding to said electrostatic charge pattern and said information on said document being copied;

u said means for transferring comprising toner backing material having a layer of toner material thereon; means for maintaining said layer of toner material on said toner backing material;

means for positioning said toner backing material with toner backing material at a point along said path.

of travel in advance of said gap;

- said electrostatic charge deposited on said toner backing material having a polarity which is opposite to the polarity of said electrostatic charge pattern on said surface; and

a quantity of powder-like toner material disposed along said path of travel at apoint intermediate said first first mentioned point and said gap whereby said electrostatic charge on said toner backing material causes a thin layer of said toner material to adhere thereto.

9. Apparatus according to claim 8 further characterized by:

said means for positioning comprises a support adjacent said gap about which said toner backing material having said layer of toner material thereon passes; and

means for depositing an electrostatic charge on said support having a polarity opposite to the polarity of said electrostatic charge on said toner backing material.

References Cited by the Examiner UNITED STATES PATENTS 2,238,479 4/1941 Senseney 118-257 X 2,803,177 8/1957 Lowrie 11717.5 X 2,820,716 1/1958 Harmon et al. 117-17.5 2,829,025 4/1958 Clemens ct a1. 2,895,847 7/1959 Mayo 118637 K 2,996,400 8/1961 Rudd et a1. 117--17.5 3,013,890 12/1961 Bixby 117-17.5

EVON C. BLUNK, Primary Examiner.

W. D. MARTIN, Examiner. 

1. APPARATUS FOR CREATING A COPY OF A MASTER DOCUMENT COMPRISING: A PHOTOCONDUCTOR AND A PLURALITY OF PROCESSING STATIONS; MEANS TO EFFECT RELATIVE MOVEMENT BETWEEN SAID PHOTOCONDUCTOR AND SAID STATIONS; A FIRST OF SAID STATIONS COMPRISING MEANS FOR ESTABLISHING A UNIFORM ELECTROSTATIC CHARGE OF ONE POLARITY ON SAID PHOTOCONDUCTOR; A SECOND OF SAID STATIONS COMPRISING MEANS FOR PROJECTING AN IMAGE OF SAID MASTER DOCUMENT ON SAID PHOTOCONDUCTOR TO CREATE AN ELECTROSTATIC CHARGE PATTERN HAVING AREAS OF RELATIVELY HIGH POTENTIAL OF SAID ONE POLARITY CORRESPONDING TO THE VISUAL INFORMATION OF SAID DOCUMENT; A THIRD OF SAID STATIONS COMPRISING A THIN LAYER OF TONER MATERIAL SPACED FROM SAID PHOTOCONDUCTOR SOLELY BY AN AIR GAP; MEANS FOR MAINTAINING SAID THIN LAYER OF TONER MATERIAL IN SPACED RELATION WITH RESPECT TO SAID PHOTOCONDUCTOR; AND ONLY SAID AREAS OF RELATIVELY HIGH POTENTIAL OF SAID ONE POLARITY ON SAID PHOTOCONDUCTOR EXERTING SUFFICIENT ELECTROSTATIC FORCES TO OVERCOME SAID MEANS FOR MAINTAINING AND CAUSING SAID TONER MATERIAL TO MOVE ACROSS SAID AIR GAP TO SAIS AREAS WHERBY TONER MATERIAL DOES NOT COME IN CONTACT WITH THE REMAINING AREAS OF SAID PHOTOCONDUCTOR AND A TONED IMAGE CORRESPONDING TO SAID VISUAL INFORMATION ON SAID MASTER DOCUMENT IS CREATED ON SAID PHOTOCONDUCTOR. 